Heat Exchanger, in Particular for a Motor Vehicle

ABSTRACT

The invention relates to a heat exchanger, in particular for a motor vehicle, having tubes and if appropriate corrugated fins through which a first, hot medium can flow and which are arranged between collecting boxes, and having at least one side part ( 1 ) which is arranged laterally between two collecting boxes, a second medium which flows around the tubes and if appropriate corrugated fins being colder than the first, hot medium during operation, the side part ( 1 ) absorbing at least some of the tensile stresses which act at least on the outermost tube as a result of different thermal expansions of the tubes and if appropriate corrugated fins, and the side part ( 1 ) having slots ( 2 ) and/or openings ( 4 ) which change the spring constant of the side part ( 1 ) in relation to a side part without slots and/or openings such that, in the event of a different longitudinal expansion of the central tubes relative to the outermost tube which is arranged adjacent to the side part ( 1 ), the tensile stress which acts on the outermost tube is reduced.

The invention relates to a heat exchanger, in particular for a motor vehicle and in particular a charge air cooler, according to the preamble of claim 1.

Heat exchangers usually have two header boxes, between which pipes, for example flat pipes, and corrugated fins are arranged. In order to connect the header boxes and to protect the outer corrugated fins, side parts are frequently arranged between the header boxes.

A problem with heat exchangers of this type, in particular with charge air coolers, is that the outer pipes are relatively cold in comparison with the central pipes and the corresponding corrugated fins, with the result that, during operation, in particular at the beginning of operation, stresses are produced in the heat exchanger as a consequence of the different temperatures and the associated different thermal expansion of the individual heat exchanger parts. Here, the outer pipes are colder, that is to say shorter, than the inner pipes and the corrugated fins, with the result that the soldered connections of the outer pipes to the pipe plates are stressed in a pronounced manner. On account of the stresses, undesired fracture formations occur, in particular in the outer pipes in the region of the soldered connections to the pipe plates.

DE 197 53 408 A1 has disclosed a heat exchanger for a motor vehicle, which heat exchanger has a fin/pipe block with a multiplicity of pipes and corrugated fins which are connected to one another in the manner of a network structure. In order to stabilize the fin/pipe block, in particular during the manufacturing process, it is surrounded on opposite sides by two side parts. A side part of this type has an approximately U-shaped profile in cross section for strength reasons, the two limbs which are bent upward serving as reinforcing ribs. For improved distribution of the thermal stresses during the operation of the heat exchanger, said reinforcing ribs according to DE 197 53 408 A1 can have expansion regions, which expansion regions are configured as fold-like beads.

According to DE 103 55 123 A1, in addition to reinforcing ribs, expansion sections are also provided, formed by apertures in the side part, which correspond with the reinforcing ribs. The reinforcing ribs are formed by a formed flat center part of the base plate of the side part, one edge of the flat center part being precut in sections for manufacture of the side part, and the flat center part subsequently being formed out of the plane of the base plate. On its longitudinal-side ends, in addition to the expansion sections, the side part can have projections which serve to cover header boxes. In order to reduce mechanical loadings, the side part has two expansion regions which are formed substantially by apertures. The latter extend transversely with respect to the longitudinal extent of the side parts over virtually the entire plane, that is to say the unbent surface of the side part.

U.S. Pat. No. 3,939,908 A1 has disclosed the provision of openings with lugs in the side part which form a means for distributing the solder, with the result that the entire surface of the side part is not soldered to the pipes/corrugated fins, as a result of which the function of elements is ensured for compensation of the different coefficients of thermal expansion and the associated different longitudinal expansion of the side part and pipes/corrugated fins, such as a fold-like bead. In the case of fold-like beads of this type which compensate for part of the stresses which are produced as a consequence of different longitudinal expansions of the pipes, tearing of the bead often occurs, however, as a consequence of overloading.

In order to avoid the tensile loadings of the pipes and to protect the pipes as a result, side parts which are divided transversely with respect to the longitudinal extent are known. Heat exchangers of this type therefore will leave some things to be desired, in particular with regard to the loading of the soldered connections of the outer pipes to the pipe plates.

It is an object of the invention to provide an improved heat exchanger.

This object is achieved by a heat exchanger having the features of claim 1. Advantageous refinements are the subject matter of the subclaims.

According to the invention, a heat exchanger is provided, in particular for a motor vehicle, having pipes and optionally corrugated fins which are arranged between header boxes and through which a first, hot medium can flow, and having at least one side part which is arranged laterally between two header boxes, a second medium which flows through the pipes and optionally the corrugated fins being colder during operation than the first, hot medium, the side part receiving at least one part of the tensile stresses which acts at least on the outermost pipe during operation as a consequence of different thermal expansions of the pipes and optionally corrugated fins, and the side part having slots and/or openings which change the spring constant of the side part with respect to a side part without slots and/or openings, in such a way that the tensile stress which acts on the outermost pipe is reduced in the case of a different longitudinal expansion of the central pipes in comparison with the outermost pipe which is arranged adjacently to the side part. As a result of the fact that the tensile stresses are reduced during operation in a targeted manner, the soldered connection between the outermost pipe and the pipe plates is protected against overloading, as a result of which tears and therefore a leak in the heat exchanger can be avoided. Here, the spring constant of the side part can be fixed by means of slots and/or openings in conjunction with the loadbearing cross section and its effective length.

If slots are provided in the side part, they preferably extend at least in regions transversely with respect to the longitudinal extent of the side part, with the result that the loadbearing cross section is reduced accordingly. The arrangement can be symmetrical or asymmetrical.

The slots are preferably configured so as to extend only over a part of the length of the side part, as a result of which the effective length of the loadbearing cross section is fixed.

The slots are preferably of H-shaped or T-shaped configuration; they are preferably arranged in the longitudinal extent and/or perpendicularly with respect to the former. In particular, an H-shaped design of the slots is preferred, the “H” being oriented in the longitudinal direction of the side part.

If openings are provided in the side part, the openings are preferably of circular and/or oval and/or ellipsoid and/or slot-like configuration. Other shapes are possible.

In cross section, the side part is preferably of flat, that is to say rectangular, or U-shaped configuration. Side parts of this type can be manufactured simply from a metal sheet by means of punching and optionally forming.

The side part preferably has at least one fin, the latter preferably extending perpendicularly with respect to the surface of the side part. The fins can be configured integrally with the side part or can be placed onto it. In the case of an integral configuration, the fin can be formed by means of bending, optionally also by means of drawing out.

The side part can comprise at least two parts which are connected fixedly to one another. In particular, fins can be attached to the side part, for example by means of welding, optionally also by means of soldering or riveting.

In its longitudinal extent, the side part preferably has a spring constant of from 1000 N/mm to 40000 N/mm. Spring constants of this magnitude result in an optimum stress reduction, in particular in the case of heat exchangers which are made from aluminum or aluminum alloys.

The heat exchanger is preferably stressfree at a uniform temperature distribution and room temperature. As an alternative, at room temperature, the side part can be under a predefined compressive stress in the direction of its longitudinal extent, that is to say the outermost pipe is prestressed somewhat.

In the following text, the invention will be explained in detail using one exemplary embodiment with a plurality of variants, with reference to the drawing, in which:

FIGS. 1 a-d show diagrammatic details of plan views of side parts having different slot patterns,

FIGS. 2 a-d show diagrammatic sections of side parts having different cross sections,

FIGS. 3 a-f show diagrammatic details of plan views of side parts having further slot patterns,

FIGS. 4 a-e show diagrammatic details of plan views of side parts having further opening patterns, and

FIGS. 5 a-j show illustrations of a further variant.

A heat exchanger, a charge air cooler of a motor vehicle in the present case, of which only parts of side parts 1 are shown in the drawing, has two header boxes according to the present exemplary embodiment, formed by trough-shaped box elements and pipe plates, a plurality of pipes, the ends of which protrude into openings which are provided in the pipe plates, and corrugated fins which are arranged between the pipes. The side parts 1 are arranged on the outside between the header boxes, for which purpose they are connected fixedly to the header boxes but not directly to the pipes and/or corrugated fins. The parts of the heat exchanger are soldered to one another in a manner which is known per se, which preferably takes place in a single soldering operation, or are connected fixedly to one another in some other way.

In order to keep stresses as low as possible between the pipe plates and, in particular, the outer pipes at the beginning of operation or at the beginning of increased loading of the charge air cooler the spring constants of the side parts are designed accordingly. That is to say, if a length difference occurs of the central, hot pipes and the outer, cold and therefore short pipes in the heat exchanger, which length difference leads to stresses, in particular in the case of the outer pipes in the region of the soldered connections to the pipe plates, the side parts compensate at least partially for these stresses by acting as a type of tie rod in the case of a temperature difference and therefore length difference of the central and the outer pipes, and counteracting the tensile stress on the outermost pipes which is caused by the adjacent, inner/central pipes as a result. Here, in contrast to the fold-like beads which are provided in conventional side parts, slots 2 or other openings are provided in the side part 1, which ensure that the spring characteristic curve, that is to say the force over the length difference of the (in particular outermost and second outermost) pipes, of the side part 1 in each case compensates for the tensile stress as a result of the innermost to second outermost pipes on the outermost pipe, substantially by a corresponding tensile stress which is oriented in the opposite direction (that is to say, a corresponding pressure on the respective outermost pipe).

Here, in a heat exchanger made from aluminum or an aluminum alloy, the spring constant D preferably lies in the range from 1000 N/mm to 40000 N/mm, it not being necessary for the spring constant to necessarily be constant in the normal operating range, that is to say it not being necessary for the spring characteristic diagram to rise in a linear manner. The spring constant or spring constants is/are fixed by the selection of the loadbearing cross section and its active length. In order to ensure the function as tie rod, it is required that a purely elastic deformation of the side part takes place over the entire operating range.

According to the exemplary embodiment, slots 2 which are arranged in an H-shape are provided in the side part 1, in order to optimize the spring constant D in the longitudinal extent of the side part 1 in such a way that the tensile stress of the side part 1, in the case of a corresponding length difference of the adjacent outermost pipes, compensates for the latter, that is to say that the force of the side part 1 on the outermost pipe compensates for the tensile stress which acts on the outermost pipe as a consequence of the length difference of the pipes, with the result that the soldered connections between the outermost pipe and the pipe plates which are arranged at both ends of the pipe, through which the force flux extends, are protected. Here, the limbs of the H extend in the direction of the longitudinal extent of the side part 1 and the transverse connection extends perpendicularly with respect to this.

According to a first variant which is shown in FIG. 1 b, T-shaped slots 2 are provided, both limbs of the T being arranged perpendicularly with respect to the longitudinal extent of the side part 1 and in a manner which is aligned with one another and ends on the side of said side part 1, and the two transverse lines being arranged in the longitudinal extent of the side part 1 and parallel to one another, said two transverse lines ending at the same level. According to a second variant, only one T-shaped slot 2 is provided, the limb of which is arranged perpendicularly with respect to the longitudinal extent of the side part 1 in a manner which ends on one side of the latter, and the transverse line is arranged in the longitudinal extent of the side part 1 in an eccentric manner with respect to the latter. In accordance with a third variant, a plurality of H-shaped slots 2 are provided which are configured in accordance with the exemplary embodiment and are arranged at the same level.

As can be seen from FIGS. 1 a-d, the cross-sectional profile of the side part 1 does not necessarily have to be constant over the entire longitudinal extent of said side part 1. This is also true of the thickness and overall width of the side part 1. The side part 1 according to the exemplary embodiment is substantially of planar configuration, that is to say apart from the end regions, in which it is soldered to the header boxes. FIG. 2 a shows a section through the latter in the region of the limbs of the H-shaped slots 2.

According to a first variant which is shown in FIG. 2 b, the two edges are bent by 90° in the longitudinal extent of the side part, with the result that the side part 2 is of U-shaped configuration. According to the illustration of FIG. 2 b, the slots 2 extend into the corner regions. As an alternative, as shown in FIG. 2 c, the slots can also extend in the base region and/or optionally also in the region of the limbs.

According to further variants, fins or edges of a side part are bent by more or less than 90°, with the result that the fins or edges are configured as oblique limbs in cross section.

FIG. 2 d shows one variant of a side part 1, in which a fin 3 which rises up perpendicularly from the surface of said side part 1 is provided approximately centrally next to a slot 2 which extends in the longitudinal extent of the side part. In the present case, this fin 3 is attached fixedly to the side part 1 by means of welding. In accordance with the preceding variant, one edge is bent over by 90° in FIG. 2 d, the edge and the fin 3 extending in the same direction.

FIGS. 3 a to 3 f show different other variants of slots 2 which are arranged, on one or both sides, obliquely or perpendicularly with respect to the longitudinal extent of the side part 1. In accordance with the illustration, the slots 2 are provided at equidistant spacings, but different spacings and/or changing angles with respect to the longitudinal extent of the side part 1 can also be provided.

According to the illustrations of FIGS. 4 a to 4 g, openings 4 are provided in the side part 1 instead of slots, it being possible for a single, circular opening 4 (cf. FIG. 4 c), a plurality of circular openings 4 which are arranged in a row or offset (cf. FIGS. 4 a, 4 b) or, for example, also oval openings 4 with a very wide variety of arrangements of the longitudinal axis (cf. FIGS. 4 d to 4 e) to be provided. Here, the longitudinal axes can also be arranged obliquely.

Any desired combinations or other designs of the openings and/or slots are possible, depending on the desired spring characteristic curve of the side part 1.

FIGS. 5 a to 5 j show one variant of the first exemplary embodiment having a side part 1, in which three slots 2 are provided which are arranged in an H-shape. Here, the slots 2 have in each case the same width which, in the present case, corresponds to approximately one twentieth of the width of the side part. In a manner which is arranged centrally with regard to the length of the side part 1, the two slots 2 which form the limbs of the “H” extend over somewhat more than one third of the entire length of the side part 1. The slot 2 which connects the two limbs is arranged in the center with regard to the length of the side part 1 and ends in the slots 2 which form the limbs. On the outside of the slot 2 which lies closest to the edge, the edge width of the side part 1 is approximately one sixth of the overall width of the side part 1.

In the present case, eight V-shaped beads 5 which extend in the longitudinal direction and the depth of which is somewhat smaller than the material thickness of the side part 1 are arranged along the center longitudinal axis of the side part 1. The length of the beads 5 is considerably smaller than that of the slots 2. In the present case, the length of the beads 5 is only approximately one third of the length of the short slot 2 which extends transversely with respect to the longitudinal extent of the side part 1. In addition to the eight beads 5 which extend in the longitudinal direction of the side part 1, two further beads 5 which are configured accordingly and are oriented parallel to the former are arranged in the edge region of the side part 1 at the level of the transversely extending limb 2.

Furthermore, in each case one opening 4 in the form of a hole having an internal diameter which is greater than the width of the slots 2 is provided in the center longitudinal axis of the side part 1 in the end region of the limbs of the “H” which is formed by the slots 2, centrally between the limb ends. 

1. A heat exchanger, in particular for a motor vehicle, having pipes which are arranged between header boxes and through which a first, hot medium can flow, and having at least one side part which is arranged laterally between two header boxes, a second medium which flows through the pipes being colder during operation than the first, hot medium, the side part receiving at least one part of the tensile stresses which acts at least on the outermost pipe during operation as a consequence of different thermal expansions of the pipes, and the side part having slots and/or openings which change the spring constant of the side part with respect to a side part without slots and/or openings, in such a way that the tensile stress which acts on the outermost pipe is reduced in the case of a different longitudinal expansion of the central pipes in comparison with the outermost pipe which is arranged adjacently to the side part.
 2. The heat exchanger as claimed in claim 1, wherein the slots extend at least in regions transversely with respect to the longitudinal extent of the side part.
 3. The heat exchanger as claimed in claim 1, wherein the slots are configured so as to extend only over a part of the length of the side part.
 4. The heat exchanger as claimed in claim 1, wherein the slots are of H-shaped or T-shaped configuration.
 5. The heat exchanger as claimed in claim 1, wherein the openings are of circular and/or oval and/or ellipsoid and/or slot-like configuration.
 6. The heat exchanger as claimed in claim 1, wherein the side part is of flat or U-shaped configuration.
 7. The heat exchanger as claimed in claim 1, wherein the side part has at least one fin.
 8. The heat exchanger as claimed in claim 1, wherein the side part comprises at least two parts which are connected fixedly to one another.
 9. The heat exchanger as claimed in claim 1, wherein, in its longitudinal extent, the side part has a spring constant D of from 1000 N/mm to 40000 N/mm.
 10. The heat exchanger as claimed in claim 1, wherein the heat exchanger is stressfree at a uniform temperature distribution and room temperature. 